摘要
酒精沼气双发酵耦联工艺既能解决蒸馏废液污染问题又能节约大量的水资源。通过前期的实验发现消化液中有抑制酒精发酵的抑制因子存在,而且酒精发酵前期硫酸的添加会抑制厌氧沼气发酵。故本文针对可能会影响双发酵循环的物质进行了研究,并寻找到解决方法,为此工艺的进一步工业化打下基础。
通过研究发现,丙酸对酒精发酵的抑制受浓度和发酵液初始pH的影响。当丙酸浓度在合适条件下能使酒精产量提高7.6%,酵母数量减少76%,甘油产量降低39.6%。但是丙酸浓度过高时酒精发酵会被完全抑制。在丙酸浓度相同时,初始pH的降低增强了丙酸对酒精发酵的抑制作用。
通过无预糖化工序的“同步糖化发酵”技术研究,将酒精发酵的初始pH提高到6.0,硫酸的消耗降低了50%,使SO42-的浓度在3g/L的沼气发酵安全范围内。高浓度酒精发酵条件为：料水(中温厌氧出水)比1：2.2(w/w),糖化酶的添加量为140 U/g木薯,发酵54 h,最终酒精浓度达14.7%(v/v)。糖化酶添加量较常规酒精发酵用量增加了17%。
在进行高浓度酒精发酵时,双发酵耦联工艺进行的没有低浓度酒精发酵时稳定,尤其在第四批到第八批时淀粉利用率仅有80%。在对厌氧发酵进行调整后循环继续到15批,发酵时间54 h,酒精度维持在14.5%左右,淀粉利用率在87%以上,比较稳定。对酒精发酵配料水进行检测发现在循环前期COD、碱度、氨氮和无机离子含量都有很大幅度的提高,后期基本稳定。
通过对钙、钠、镁、钾四种离子对酒精发酵的影响进行研究发现,钙离子的抑制浓度为10 g/L,钠离子的抑制浓度为5 g/L,镁离子浓度在5g/L以下时会提高最终酒精产量,而钾离子对酒精发酵的影响并不明显。
The practiced of ethanol-methane coupled process, could save plenty of water resources, and prevent wastewater discharging to the environment. We detected that there were inhibitors, which have negatively effect on the ethanol fermentation, in the anaerobic digestion effluent. The SO42-, which joined in the system to ensure that the mash adjusted to pH 4.0-4.2, would be harmed to the methane fermentation. As a result, we studied the inhibitors which would be have negatively effect on the ethanol-methane coupled process, and found solutions to the problems. This paper provides fundamental base for the further industry production of the ethanol-methane coupled process.
The effect of propionic acid on the ethanol fermentation depend on the concentration of propionic acid and the initial medium pH. Under the moderate concentration of propionic acid, the final ethanol concentration increased 7.6%compared to the control. Conversely, the biomass production decreased 76%, the glycerol production decreased 39.6%compared to the control as well as. However, when the propionic acid was high, the ethanol fermentation was inhibited totally. At the same concentration of propionic acid, the inhibition of propionic acid to the ethanol fermentation would be enhanced with the pH of the mashing depressed.
The dosage of sulfate reduced by 50%through elevating the initial medium pH to 6.0 in the simultaneous saccharification and fermentation (SSF) without pre-saccharification, resulted in the concentration of sulfate under 3 g/L, which was safe to the methane fermentation. The very high gravity ethanol fermentation conditions:cassava mixed water at 1:2.2 (w/w) ratio, the dosage of glucoamylase was 140 U/g cassava, fermentation time 54 h, and the final ethanol concentration was 14.7%(v/v). In the optimized process, the glucoamylase dosage increased 20 U/g cassava compared to that in the traditional process.
The VHG ethanol fermentation not gone as well as the regulation when the ethanol-methane coupled process working, especially, at the fourth to eighth batch, the starch utilization rate was only 80%. However, the cycle went more stable after the methane fermentation rearranged. This cycle has been operated 15 batches, the fermentation time was 54 h, the final ethanol concentration was above 14.5%(v/v), and the starch utilization rate was above 87%. The performance of the water for mashing had been rapidly accumulated at the prophase of the cycle, however, which had been stabled after the methane fermentation rearranged, such as the concentration of COD, NH4+-N, alkalinity and the concentration of inorganic ions.
The effect of inorganic ions, such as Ca2+, Na+, Mg2+, K+, on the ethanol fermentation were determined. It was shown that the inhibit concentration of Ca2+was 10 g/L, and the inhibit concentration of Na+was 5 g/L. The final ethanol concentration had been increased when the concentration of Mg2+below 5 g/L, and the effect of K+ on the ethanol fermentation was not obvious.
引文
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